<template>
  <div class="pagination">
    <button
      :disabled="currentPage === 1"
      @click="$emit('changePage', currentPage - 1)"
    >
      上一页
    </button>
    <button
      v-if="startEndPage.start > 1"
      :class="{ active: currentPage === 1 }"
      @click="$emit('changePage', 1)"
    >
      1
    </button>

    <button v-if="startEndPage.start > 2">···</button>

    <button
      :class="{ active: page === currentPage }"
      v-for="page in filterPages"
      :key="page"
      @click="$emit('changePage', page)"
    >
      {{ page }}
    </button>

    <button v-if="startEndPage.end < totalPage - 1">···</button>
    <button
      v-if="startEndPage.end < totalPage"
      :class="{ active: currentPage === totalPage }"
      @click="$emit('changePage', totalPage)"
    >
      {{ totalPage }}
    </button>
    <button
      :disabled="currentPage === totalPage"
      @click="$emit('changePage', currentPage + 1)"
    >
      下一页
    </button>

    <button style="margin-left: 30px">共 {{ total }} 条</button>
  </div>
</template>

<script>
export default {
  name: "Pagination",
  props: ["currentPage", "totalPage", "continuePage", "total"],
  computed: {
    startEndPage() {
      let start, end;
      //先判断临界值如果连续页长度大于页码总长度:起始是1 结束是总长度
      if (this.continuePage >= this.totalPage) {
        start = 1;
        end = this.totalPage;
      } else {
        //如果连续页小于总也数,先计算出来连续页的开头和结尾
        start = this.currentPage - Math.floor(this.continuePage / 2);
        end = this.currentPage + Math.floor(this.continuePage / 2);

        //判断临界值,如果start<1 则start只能最小是1
        if (start < 1) {
          start = 1;
          end = this.continuePage;
        }

        //判断临界值,如果end>total,则end最大只能是total
        if (end > this.totalPage) {
          end = this.totalPage;
          start = this.totalPage - this.continuePage + 1;
        }
      }

      console.log(start, end);
      return {
        start,
        end,
      };
    },
    //因为v-if和v-for不能一起使用,所以我们可以根据条件,把v-for需要真正遍历出来的值一次放入数组中
    //未来在组件中直接遍历数组即可
    filterPages() {
      const arr = [];
      for (var i = 1; i <= this.startEndPage.end; i++) {
        if (i >= this.startEndPage.start) arr.push(i);
      }
      return arr;
    },
  },
};
</script>

<style lang="less" scoped>
.pagination {
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
</style>
